The present invention relates to increasing the efficiency of cooling of a heated surface.
Currently, great efforts are being made to increase the operating capabilities of computers. One of the elements limiting the speed and efficiency of computers is heat build-up. The efficient and uniform cooling of electronic components is one of the most crucial limiting factors in the design and operation of modern electronic devices. For example, one of the factors limiting the speed and efficiency of operation of computers is the computer chip temperature (i.e., the efficiency and speed decrease as the temperature of the computer chip rises). Accordingly, tremendous efforts have been made to remove heat from computers and computer chips so as to increase their operating capabilities.
The current technology for the cooling of electronic components is basically restricted to convective cooling using a single-phase fluid (gas or liquid). In convective cooling, the driving force for heat transfer is the temperature difference between the fluid and the heated surface.
Conventional single-phase convection cooling does not provide high heat flux while, at the same time, maintaining a low surface temperature of the object cooled. The dual objectives of high heat flux and low surface temperature are essential for the development of future generations of ever more powerful computer chips.
One way to increase heat flux is through the use of liquid convective cooling with boiling. Unfortunately, the surface temperature must remain high for boiling to occur. Another problem with liquid convective boiling is the hysteresis of incipient boiling temperature overshoot. Hysteresis of incipient boiling temperature overshoot is particularly a problem when dielectric fluorocarbon liquids are used as the working medium.
An additional problem with boiling is its discrete nature in both space and time (for example, nucleate boiling) which can result in the non-uniform cooling of the circuit board and the undesirable consequence of creating an increase in the level of electronic noise.
Another method of cooling includes the placing of an electronic circuit board in an enclosure filled with a heat-conducting liquid. Heat is conducted from the chips through the heat-conducting liquid, and in some instances also through the heat-conducting structure, to an outside surface which in turn is to be cooled by conventional single-phase convective cooling. Unfortunately, this method suffers from the aforementioned shortcomings of conventional single-phase convective cooling.
A research proposal to the National Science Foundation entitled, "A Combined Experimental and Theoretical Study of Mist Cooling of a Heated Surface" was released in December of 1984. The publication disclosed the cooling of a flat heated surface by the evaporation of a liquid film from the heated surface, which was maintained by the deposition of droplets from a mist flow. However, the disclosed cooling is limited to flat surfaces.
In 1978, an IBM Technical Disclosure Bulletin disclosed a method of cooling integrated circuit chips by the application of a liquid jet to a deflector in contact with the integrated circuit chip. The deflector has a concave area in which the liquid jet impinges. The jet strikes the deflector, spreads radially outward and forms a thin film region which changes into a thick, slowly moving layer as it approaches the outer region of the deflector. The jet system cools an array of chips. The nozzles of the jet system are fed from a common manifold and the nozzle diameters are chosen to reflect the heat transfer requirements for individual chips. Relatively narrow orifices may be used for low heat dissipation and relatively wide orifices may be used for high heat dissipation. However, the amount of heat removed by the device disclosed in the IBM Technical Bulletin is limited. Further, the use of a deflector requires special manufacturing techniques and increases the costs of manufacture.
U.S. Pat. No. 3,887,759 to Staub discloses an evaporative cooling system employing liquid film evaporation from a grooved evaporative service. In the system, a vaporization chamber houses the apparatus to be cooled (for example, a transformer). The film of liquid flows over a heated surface of the apparatus and is evaporated thereby, cooling the apparatus. The film receives fluid from condenser tube openings which drip fluid onto the surface to be cooled. The surface of the apparatus has shallow grooves which stabilize the distribution of the flowing liquid so that all sections of the surface are maintained in a wet condition by the flowing film. The grooves maintain the film of liquid intact so that the film will not break into rivulets (as would be the case with a smooth surface), thereby preventing rupture of the film. However, the system of Staub requires the use of a grooved evaporative surface and a vaporization chamber. Hence, the unit of Staub is bulky and requires special manufacturing techniques which, in turn, increases the cost. Further, the system of Staub cannot simultaneously provide a high heat flux combined with a low surface temperature.
U.S. Pat. No. 3,794,886 to Goldman discloses a fluid-cooled semiconductor socket. The semiconductor device is placed in contact with a thermally-conductive plate which conducts heat away from the semiconductor chip. The semiconductor chip is in thermally-conductive contact with a portion of the semiconductor case which contacts the surface of the plate. A thermally-conductive fluid conduit is attached to the plate on a face directly opposite from the semiconductor chip. The conduit is placed so as to maximize thermal conductivity between the point where it is placed on the plate and the semiconductor chip. The fluid flowing through the conduit absorbs and conducts away heat produced by the semiconductor chip. However, the device of Goldman is inefficient, requires the use of a fluid flowing through the conduit to remove heat and generally suffers the drawbacks associated with single phase convective cooling.
U.S. Pat. No. 4,109,707 to Wilson, et al. discloses a fluid-cooling system for electronic systems particularly adapted to cool large scale integrated circuit chips mounted on substrates. The system has one or more heat exchangers through which a liquid coolant is circulated. Each heat exchanger has a flexible wall and is mounted so that its flexible wall is in close proximity to a surface of a substrate to be cooled. The heat exchange medium includes silicon oil, ethylene glycol, freon and water. However, the device of Wilson, et al. is a single-phase liquid cooling system and hence, cannot provide a high heat flux in combination with a low surface temperature.
It is, therefore, an object of the present invention to provide an efficient and inexpensive method for the cooling of computer chips as well as all other heated surfaces having cavities.
Other and further objects will become apparent to those skilled in the art upon reading the present specification, and it is not intended in any way to restrict the scope of the invention by setting forth the objects above.